In scroll machines such as compressors there are two scroll members which must be held to relative orbiting motion. Commonly, one of the scroll members is called a fixed scroll and the other scroll member is called an orbiting scroll. An Oldham coupling can be employed to hold the fixed and orbiting scrolls to a relative orbiting motion. To achieve this, the Oldham coupling reciprocates with respect to the crankcase while the orbiting scroll reciprocates with respect to the Oldham coupling. The coactions are those of slots and keys and the Oldham coupling surrounds the hub of the orbiting scroll and possibly the axial compliance or support structure. Movement of the Oldham coupling usually takes place within diameters. When considering the need to keep the keys in their slots for their full strokes and the need to avoid interfering with the axial compliance or support structure, there can be a significant increase in the envelope required to contain the Oldham coupling and the housing in which it is located. Alternatively, there can be a significant reduction in the envelope available for the axial compliance or support structure.
European Patent Application 0 479 412 A1 discloses an Oldham coupling of an oval shape with one pair of keys located on a chord of a circular section of the oval but located on "outwardly projecting flange portions". These projecting flange portions extend beyond the diameter of the circular section. This achieves some reduction in the required envelope by positioning the keys in regions where more operating space may be available.